The mineral processing industry uses a number of different methods to separate the desired minerals from other minerals and rocks. One such mineral processing system similar to that shown in FIG. 1 includes a mineral crusher, which crushes rocks and minerals to a size that is appropriate for the type of mineral being processed (approximately 250 μm for sulfide copper). The crushed rock and mineral is combined with water, a reagent, a frother, and a PH control to make a two-phase slurry (liquid and solids). This slurry is pumped into a mechanical flotation tank 1 for separation of the desired mineral (e.g., copper) from the other minerals and rocks. Gas is introduced at the bottom of the tank that is then chopped and mixed with the slurry by an impeller or mixer 2. This produces a means of floating minerals to the surface for extraction while sending other minerals to the bottom of the tank to exit through the tailings line 3. In some cases the desired mineral is floated to the surface, and in other cases it is recovered in the tailings. In the case where the desired mineral is floated, the proper reagent is selected to enable the mineral to attach to the rising bubbles 4. The bubbles then carry the mineral to the top of the flotation tank to thereby create a froth layer 5 with the desired mineral, which then is piped away or allowed to overflow into another receptacle.
Another method of separating the desired mineral from other minerals and rocks includes a column cell 6 similar to that shown in FIG. 2, which is another type of flotation machine that is sometimes used in combination with the mechanical flotation tank. In the column cell 6, the slurry is introduced at the top of the collection zone and flows down the column towards the bottom. Gas bubbles 4 are introduced at the bottom of the collection zone and slowly rise to the froth layer at the surface. The bubbles are generated using a sparging process. There is no mechanical agitation. The gas is typically expanded through a set of nozzles 7 to create bubbles, which can be accomplished either internal or external to the column. At the surface of the froth layer, wash water is sprayed down on the surface of the froth to control the bias in the column. As in the mechanical tank 1, the minerals in the froth layer 5 are collected in an overflow channel for further processing.
The amount and size of the bubbles 4 as well as the flow rate of the bubbles to the surface of the flotation tank/column cell are important parameters to know and control to provide the most efficient separation process of the ore. It would be advantageous to provide a submersible meter that can measure the gas holdup (i.e., gas volume fraction) of the fluid flowing from the bottom to the top of the tank, as well as the flow rate of the aerated fluid.